Process for preparing microporous,open-celled cellular polyamide,polyester and polyacetal structures

ABSTRACT

A process for preparing microporous, open-celled cellular polyamide, polyacetal and polyester structures which comprises (a) dissolving the starting polymer in formic acid, hexafluoroisopropyl alcohol, hexafluoroacetone hydrate or mixtures thereof; (b) dispersing in the resulting solution a liquid chlorofluorocarbon; (c) cooling the dispersion to at least the solidification temperature of the chlorofluorocarbon; and (d) removing the chlorofluorocarbon from the dispersion at a temperature of from about 0* C. to the solidification temperature of said chlorofluorocarbon.

nite States Patent Jenkins PROCESS FOR PREPARING MIC ROPOROUS,OPEN-CELLED CELLULAR POLYAMIDE, POLYESTER AND POLYACETAL STRUCTURESlnventor: Francis Edward Jenkins, Wilmington. Del.

Assignee: E. l. du Pont de Nemours and Company,

Wilmington, Del.

Filed: Dec.23,1970

Appl. No.: 101,172

U.S. Cl ..260/2.5 M, 260/31.2 N, 260/31.2 R, 260/3l.2 XA, 260/32.8 N,260/32.8 R, 260/33.4 R, 260/33.8 R

Int. Cl ..C08j 1/26, C08j 1/28 Field of Search ..260/2.5 M

References Cited UNITED STATES PATENTS Murata ..260/2.5 M

July 4, 1972 FOREIGN PATENTS OR APPLICATIONS 1,138,121 12/1968 GreatBritain ,.260/2.5 M

Primary Examiner-Murray Tillman Assistant Examiner-Morton FoelakAttorney-Nicholas J Masington, Jr.

[57] ABSTRACT 17 Claims, No Drawings BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to a novel process formaking microporous,open-celled cellular structures of polyamides,polyesters, and polyacetals in the presence of selectedchlorofluorocarbons.

2. Prior Art Cellular polymeric structures are well known in the art andhave found extensive use as insulating materials, constructionmaterials, packaging and the like. Such cellular structures have beenmade from a variety of polymers, including polyurethanes, polystyrene,cellulose esters, and polyvinyl chloride.

A number of methods are available for the preparation of polymericcellular structures. In one method, a molten thermoplastic polymericmaterial is thoroughly mixed with a gas or a volatile liquid, and themixture is heated in a closed chamber under pressure. The hot mixture isthen released from the closed chamber through a suitable die or opening.At lower pressure, the gas or the low boiling liquid expands andvolatilizes, leaving a permanent cellular structure on cooling.

In another method, molten thermoplastic polymer is thoroughly mixed withsolids of finite size which after cooling are subsequently extractedfrom the polymer mass with selected solvents, leaving behind a cellularstructure.

Still another method is to compact a powdered or granular polymer at atemperature slightly below its melting temperature, thus forming aninterstitial polymer sn'ucture.

In yet another method, the polymer is dissolved in a hot liquid which isnot a good solvent for the polymer at room temperature. The solutionthen is cooled, and the solvent is removed by leaching with water or bydistillation at reduced pressure (cf. U.S. Pat. No. 3,427,179 to W. J.Davis).

An additional method, which is often used in the preparation ofmicroporous cellular sheet or film, consists in treating a solution of apolymer with a liquid which is miscible with the polymer solvent but isa nonsolvent for the polymer, thereby coagulating the polymer. Thecoagulating liquid is then removed, leaving behind a porous cellularsheet or film of the polymer.

There are, however, various disadvantages manifested by these processes.Some processes, for instance, are suitable only for thermoplasticpolymers which are stable in the molten state. The most apparentlimitation of the prior art methods of forming cellular structure is theinability of each method to cover a broad variety of shapes of cellularmaterials. Coagulation of a polymer from a solution with a nonsolvent,for example, is most practical for production of porous cellular sheetsor films but is of no practical use in forming other shapes.

The cellular material prepared by the above methods is eitherclosed-celled or open-celled. Closed-celled structures containindividual cells whose size and cell wall thickness depend upon suchfactors as molecular weight of the polymer, type of blowing agent used,and the density of the final cellular material. The open-celledstructure does not contain individual cells but is characterized by thepresence of interconnecting channels throughout the cellular structure.Closedcelled polymeric materials are especially suitable for thoseapplications where the transmission of vapor would be undesirable, suchas in thermal insulation. Open-celled polymeric materials, on the otherhand, are especially suitable for those applications where transmissionof vapor would be desirable. Microporous open-celled polymericmaterials, such as certain polyurethane foams have found acceptance assynthetic leather-like poromeric structures.

While closed-celled polymeric materials can be readily made by knownmethods of the art, open-celled polymeric structures are usually muchmore difficult to' obtain. There is therefore a need for a reliable andconvenient process for making open-celled polymer materials of anydesired shape and this need is satisfied by the process of the presentinvention.

SUMMARY OF THE INVENTION The present invention is directed to a processfor preparing microporous open-celled cellular structures from a polymerselected from polyarnide, polyacetal and polyester.

The process comprises the following steps:

a. dissolving at least 0.3 weight per volume percent of a normally solidpolyarnide, polyacetal or polyester in formic acid, hexafluoroisopropylalcohol, hexafluoroacetone hydrate or mixtures thereof to form a polymersolution with the proviso that formic acid is utilized either alone orin mixture only when the selected polymer is polyamide;

b. dispersing in the resulting solution from about equal to about tentimes its volume of a liquid chlorofluorocarbon or mixture ofchlorofluorocarbons having a boiling point in the range of from about 10to 150 C., a melting point in the range of from about -40 to C. (meltingpoint being lower than boiling point), an entropy of fusion of less than10 calories/K/mole (heat of fusion [caL/mole] /temperature of fusion[K]), a plastic flow index of at least 0.1 g./ 10 min. at the reducedtemperature of 0.96 to 0.99 (reduced temperature equals 'I K at whichflow measured/T K of melting point; plastic flow being a measurement ofthe rate of extrusion as measured on a plastometer according to ASTM-Dl238-65T) and a solubility in water of less than about 2 weight percent,to form a liquid dispersion, at a temperature below the atmosphericboiling point of the lowest boiling component of the polymer solution;

c. cooling the dispersion to at least the solidification temperature ofthe lowest melting chlorofluorocarbon present, thus causing thedispersed chlorofluorocarbon to solidify; and

d. removing both the solvent and the chlorofluorocarbon therefrom at atemperature of from about 0 C. to the solidification temperature of thechlorofluorocarbon.

DESCRIPTION OF THE INVENTION these goups being integral members of thelinear polymeric chain. Polymers of this type are well known in the art.Polya mides may be derived from dibasic acids such as oxalic, succinic,adipic, suberic, and sebacic and diamines such as ethylenediarnine,pentamethylenediamine, hexamethylenediamine, decamethylenediamine,tetradecamethylenediamine or di(p-aminocyclohexyl)methane. A polyamidecan also contain one or more aromatic groups either in its acid portionor its amine portion, as, for example, inpoly(p-phenyleneterphthalamide), orpoly(mphenyleneisophthalamide/terephthalamide). Polyamides can also bederived from monoaminomonocarboxylic acids or their cyclic lactams.Typical examples of such polymers are polycaprolactam (Nylon 6) andpoly( l l-aminodecanoic acid).

A polyester is defined as synthetic, linear, condensation type polymerwhose repeating units contain the ester group,

these groups being integral members of the linear polymer chain.Polyesters are well known in the art. Polyesters may be those derivedfrom aliphatic dibasic acids such as oxalic, succinic, glutaric, adipic,and sebacic and glycols such as ethylene glycol, propylene glycol,trimethylene glycol, hexarnethylene glycol, and decarnethylene glycol;from aromatic dicarboxylic acids such as terephthalic acid andisophthalic acid and ethylene glycol; or from hydroxy acids such ashydroxypivalic, a-hydroxyisobutyric, w-hydroxycaproic orw-hydroxydecanoic acids.

A polyacetal is defined as synthetic, high molecular weight, linearpolymer containing acetal oxygens as integral part of the linearpolymeric chain. These polymers are characterized by the presence of therepeating acetal unit Polyacetals are well known in the art.Polyoxymethylene or polyformaldehyde, and particularly polyoxymethylenestabilized by acylation of its terminal hydroxyl groups are well known.

Polyamides, polyesters and polyacetals which are normally solid and,therefore, of high molecular weight are in general poorly soluble inmost organic liquids. Thus, the polymers useful in the process of thepresent invention are insoluble in conventional solvents such asmethanol, ethanol, isopropyl alcohol, dioxane, trioxane,tetrahydrofuran, acetone, and methyl ethyl ketone.

Each of the above polymers can, however, be dissolved in at least one ofthe following solvents: formic acid, hexafluoroisopropyl alcohol, andhexafluoroacetone hydrates.

Formic acid is a commonly available commercial product.Hexafluoroisopropyl alcohol, or specifically 2H-hexafluoro-2- propanol,can be made by the reduction of hexafluoroacetone either by the methodof Middleton described in US. Pat. No. 3,418,337 or by the method ofSwamer described in US. Pat. No. 3,468,964.

Hexafluoroacetone is commercially available. It forms two hydrates,namely the monohydrate (perfluoro-2,2- propanediol) melting at 79 C.,and a liquid sesquihydrate. While the sesquihydrate is more practical touse as a solvent and is more stable, both hydrates dissociate on heatingwith formation of water and free hexafluoroacetone. The latter is atoxic gas under normal temperature and pressure conditions. It is,therefore, recommended that heating of hexafluoroacetone hydrates beavoided and that these materials be used with adequate ventilation.

All the above solvents form strong hydrogen bonds, and this propertycontributes to their good dissolving power for polar polymers, such asthose contemplated by the process of the present invention. In addition,all these solvents are soluble in or" miscible with water, but areimmiscible with the chlorofluorocarbons useful in the present process.

It is necessary for the successful operation of the present process thatthe polymer be soluble in the selected solvent to the extent of at least0.3 percent (w/v), since cellular structure obtained from a polymersolution of any lower concentration would be too fragile and friable forpractical applications. It also would be too costly to handle largevolumes of very dilute solutions and to remove and recover the solvent.

Since the void, i.e., porosity, content of the cellular structure ispartially determined by the concentration of the polymer solution in theprocess of this invention, it is undesirable to use polymer solutionwhose polymer concentration is so high as to give cellular structureswith a void content of, say, less than about 2 percent. Such cellularmaterial while still microporous and open-celled would be almostindistinguishable from the original bulk polymer in physical properties.It is therefore preferable that the polymer concentration not exceedabout 50 percent (w/v).

High molecular weight polyamides are soluble in all three solvents, i.e.formic acid, hexafluoroisopropyl alcohol, and hexafluoroacetonehydrates. Dissolution in fonnic acid is slow at room temperature, butcan be accelerated by heating. High molecular weight polyesters andpolyacetals are not sufficiently soluble in formic acid. Both classes ofpolymers are, however, very soluble in hexafluoroisopropyl alcohol andin hexafluoroacetone hydrates.

The chlorofluorocarbons useful in the process of this invention shouldpossess the following characteristics: (1) a boiling point in the rangeof from about 10 to 150 C.; (2) a melting point in the range of fromabout 40 to 125 C. (melting point being lower than boiling point); (3)an entropy of fusion of less than 10 calories/K/mole (heat of fusion[cal/mole] /temperature of fusion [K]); (4) a plastic flow index of atleast 0.1 g./l0 min. at the reduced temperature of0.96 to 0.99 (reducedtemperature equals T K at which flow measured/T K of melting point;plastic flow being a measurement of the rate of extrusion as measured ona plaritomctcr according to ASTM-D l238-65T), and (5) a solubility inwater ofless than about 2 weight percent.

The preferred chlorofluorocarbons of this invention include 1, l l,2,2-pentachloro-2-fluoroethane, l,l,2,2-tetrachloro-1,2-difluoroethane, l, l l ,2-tetrachloro-2,2-difluoroethane, l, ll-trichloro-2,2,2-trifluoroethane, l,2-dichlorodecafluorocyclohexane, ll ,2,2-tetrachloro-perfiuorocyclobutane, 1 ,2-dichloroperfluorocyclobutane, l-chloroperfluorocyclo butane,1,1,2-trichlorol ,2,2-trifluoroethane, l, l l ,3-tetrafluoro-2,2,3,3-tetrachloropropane, l, l l,3,3-pentafluoro-2,2,3-trichloropropane, l,l,l,3,3,3-hexafiuoro-2,2-dichloropropane, 1,1,l,4,4,4-hexafluoro-2,2,3,3- tetrachlorobutane andmixtures thereof. The melting points and the boiling points of thesechlorofluorocarbons are shown in Table 1 below.

TABLE I Melting Boiling point. point, Chlorolluorocarbon C. 3 C

CCh-CChF CCl2FCClzF, 33.5 CClg-CCiFy s r -10. '1 CCl FCClF -35. CC13CF2i H CFr-CCltr-CCizF. 41. T CF;CCl2CClFz... t. CFg-CClrCFg. 3.CF3CC]g-CCizCF3.. b5. '1 iFz-CFg-CCirCCiz 84.

(iF CF CClFCClF 15.1 561.!

CF (JF CF CClF 3'a. 1 25. 6

TABLE 11 Wt. Freezing Point of CCl ,CClF CCl CClfi/CCl F CCl,F

in mixture mixtures, C.

it is thus possible and often advantageous to use a mixture ofchlorofluorocarbons in the process of this invention. The preferredchlorofluorocarbon is l,l,l,2-tetrachloro-2,2- difluoroethane. Thepreferred mixture of chlorofluorocarbons is a mixture of1,1,l,2-tetrachloro-2,Z-difluoroethane andl,1,2,2-tetrachloro-1,2-difluoroethane. Both are solid at roomtemperature, yet can be removed by evaporation under very mildconditions.

The chlorofluorocarbons suitable in the present process are immisciblewith, or at most very slightly soluble in formic acid,hexafluoroisopropyl alcohol, or a hexafluoroacetone hydrate, which arethe polymer solvents employed in this process.

In the process of this invention, a polyamide, polyester or polyacetalhaving a solubility of at least 0.3 percent (weight/volume) is dissolvedin a solvent selected from the group consisting of formic acid,hexafluoropropyl alcohol and hexafluoroacetone hydrate, with the provisothat if formic acid solvent alone or in mixture with any of the othersolvents is utilized, only a polyamide will be dissolved therein.Mixtures of two or more of these solvents may be used. Therefore, atleast 0.3 weight per volume percent of the polymer is dissolved in theselected solvent. Heating, either at atmospheric or autogeneouspressure, usually facilitates the dissolution.

The chlorofluorocarbon to be used is then added with agitation at atemperature below the atmospheric boiling point of the lowest boilingcomponent of the polymer solution. The chlorofluorocarbon must be liquidat the time of addition and thus is usually first heated above itsmelting point.

The resulting dispersion is cooled by any art-known means withcontinuing agitation until a thick paste-like mixture is obtained. Thisoccurs at or below the solidification temperature of the lowest meltingchlorofluorocarbon present thus causing the dispersed chlorofluorocarbonto solidify. This paste-like mixture can be shaped, molded, pressed orextruded.

The chlorofluorocarbon and the polymer solvent may be removed undervacuum at a low temperature leaving behind a microporous, cellularstructure of the polymer whose shape and dimensions are essentiallythose of the original polymer dispersion.

Since both the chlorofluorocarbon and the polymer are insoluble inwater, while the polymer solvent is very soluble, it is also possible totreat the cooled dispersion with cold water to precipitate the polymer.A solvent-water phase and a mixture of the polymer and solidchlorofluorocarbon results. The solvent-water mixture is then removed byany conventional method, such as, e.g., decantation or filtration,leaving behind an intimate mixture of the polymer and the solidifiedchlorofluorocarbon. Such intimate mixture of the polymer and thechlorofluorocarbon is plastic and malleable and may also be molded,pressed, shaped or extruded.

The chlorofluorocarbon may be removed from this intimate mixture bysublimation at a temperature of from about C. to the solidificationtemperature of the chlorofluorocarbon giving an open-celled structure ofa high void content. While the sublimation can be carried out at anyeffective temperature, it is most efficient to operate at about 35 C.below the solidification temperature of the chlorofluorocarbon.

The chlorofluorocarbon may also be separated from the intimate mixtureof the polymer and the chlorofluorocarbon by aspiration at a temperatureabove the solidification temperature of the chlorofluorocarbon but belowits atmospheric boiling point. In this procedure the liquidchlorofluorocarbon is first aspirated rapidly, removing substantiallyall of the chlorofluorocarbon and the residual chlorofluorocarbon isvaporized away from the polymer. Removal of the chlorofluorocarbon byaspiration usually results in a microporous structure which has a lowervoid content than that produced by the sublimation procedure.

While only chlorofluorocarbons are discussed herein, it is recognizedthat other non-chlorofluorocarbon solvents, e.g., cyclohexane, couldlikewise be utilized in the process of this invention; however, theylack the efiicacy manifested by chlorofluorocarbons meeting theparameters set out herein.

A very important and valuable feature of this invention is that aplastic, pliable, moldable, solidified chlorofluorocarbon is obtained oncooling, and that a plastic, pliable, moldable and extrudable intimatemixture of the polymer with the solidified chlorofluorocarbon isobtained on adding water to the chilled dispersion. The above plasticand pliable mixtures may be partially oriented by rollingunidirectionally or bidirectionally to provide a cellular structure withimproved strength in the direction of orientation. These mixtures thuscan be formed and processed in many ways. They can be, for example:

1. extruded, molded or shaped into any desired shape and then convertedinto a cellular structure which will have the shape and the dimensionsof the original mixture;

2. coated on Supports of various types and then converted to amicroporous, open-celled, supported cellular structure;

3. layered on top of a plastic mixture of another polymer, thenconverted to a laminated cellular structure;

4. milled with a finely divided solid, then converted to a cellularstructure containing uniformly dispersed solids;

5. partially oriented by shearing, rolling, or stretchingunidirectionally or bidirectionally, then converted to a partiallyoriented cellular structure.

It is also possible to prepare particulate microporous cellularstructures which have the appearance of finely divided polymer powder bya slight variation in the above-described process. Each particle,however, has open-celled microporous structure and, consequently, a verylarge surface area. The present invention thus provides a convenient anduseful method for preparing either a coherent microporous cellularstructure or a particulate microporous cellular structure. It is to benoted that with many polymers, especially those which have bothtoughness and high elongation, polymer powders are obtained with greatdifficulty by the usual grinding process. Generally, grinding must becarried out at low temperatures, e.g., Dry Ice temperature or evenlower.

The particulate, microporous, cellular, polymeric structures areprepared by adding to the warm dispersion of the chlorofluorocarbon andthe polymer solution a surfactant in an amount of up to 3 percent (w/v)of the chlorofluorocarhon/polymer solution mixture and cooling and thenadding water as described previously. Removal of both thechlorofluorocarbon and the polymer solvent from the chilled semisoliddispersion in the manner previously described results in the formationof the particulate polymeric material. The surface active agents usefulin the present invention are well known in the art. The suitable classesinclude:

1. anionic surface active agents which include, for example, fattycarboxylic acids, sulfuric esters such as sulfated alcohols and olefins,alkanesulfonic acids and alkylarylsulfonic acids;

2. cationic surface active agents which include, for example, fattyamines and quaternary ammonium compounds; and,

3. nonionic surface active agents which are generally products in whicha controlled number of ether or hydroxyl groups is introduced into ahydrophobic molecule. Representative nonionic surface active agentsinclude polyoxyalkylene ethers of higher fatty alcohols and alkylphenolssuch as octlyphenoxypolyethoxyethanol.

Useful surface active agents must be soluble in the chlorofluorocarbons.Use of larger quantities of a surface active agent, i.e., more thanabout 3 percent (w/v) is undesirable because (1) no improvement ofresults is observed at that level, and (2) there is a risk of possiblegelation of the polymer solution.

It is also sometimes possible to obtain microporous particulatestructures even without the use of any surfactant. This is especiallytrue of polyesters and polyacetals. Although the physical interactionsamong the various components of the mixtures are not well understood, itappears that the particulate material tends to form more readily whenthe ratio of chlorofluorocarbon to polymer in the mixture is high.Conversely, when this ratio is low, coherent structures result. However,a skilled chemist can easily determine the proper amounts of theingredients required to obtain the desired structure, coherent orparticulate. As a rule, however, the use of surfactant in an amount upto 3 percent (w/v) results in cellular structures which are of a smallerand more uniform size than those obtained in the absence of thesurfactant.

. The process of the present invention thus provides a novel method ofpreparing cellular structures of polyamides, polyesters and polyacetalswhich are open-celled and microporous. Among the advantages of thepresent invention over the prior art methods are:

l. a convenient and safe range of processing temperatures whicheliminates or minimizes heat degradation of the polymeric material;

2. excellent control of the porosity of the cellular structures;

3. adaptability to the preparation of particulate cellular structures;

4. formation of cellular structures that are open-celled andmicroporous;

5. excellent versatility in forming shaped cellular structures.

The process of the present invention is conveniently carried outbatchwise. However, it will be readily apparent to those skilled in theart that the steps in the present invention are readily adaptable to acontinuous process.

EXAMPLE 1 Microporous Open-Celled Structure of Polyoxymethylene Solidpolyoxymethylene (polyformaldehyde), 2.0 g. was dissolved in 15 ml. ofhexafluoroisopropyl alcohol. To the solution, 20 ml. of liquidl,l,l,2-tetrachloro-2,2-difluoroethane (m.p. 40.6 C.) were added, andthe mixture wasstirred vigorously. On cooling the mixture in an icewater bath with continuing stirring, there was obtained a thick,paste-like mixture. This material could be shaped, extruded, or pressed.A portion of the above, mixture was placed in a small aluminum cup,which was then placed in a conventional laboratory vacuum sublimator.The outer wall of the sublimator was cooled with ice water to C., andthe condensation surface for the chlorofluorocarbon and thehexafluoroisopropyl alcohol was cooled to 78 C. with a Dry Ice-acetonemixture. Subjecting the chilled mixture in the sublimator to a vacuum ofapproximately 1 mm. Hg. for 30 minutes, produced a microporousopen-celled coherent structure of polyoxymethylene which still retaineda small portion of hexafluoroisopropyl alcohol, which could be detectedby its odor. This small residual amount of hexafluoroisopropyl alcoholwas removed by placing the cellular material in a vacuum oven at 30 C.for minutes. The final product was a coherent, microporous, open-celledpolyoxymethylene, which was white and somewhat brittle.Hexafluoroacetone hydrates, used instead of hexafluoroisopropyl alcohol,give comparable results.

EXAMPLE 2 Microporous, Open-Celled Sheet amethyleneadipamide) Solidpoly(hexamethyleneadipamide), g., was dissolved in 200 ml. ofhexafluoroisopropyl alcohol. To 20 ml. of this polyamide solution, 40ml. of liquid l,l,l,2-tetrachloro-2,2- difluoroethane was added, and themixture was stirred vigorously. On cooling the mixture in an ice bathwith continuing stirring,there was obtained a thick paste-like mixture.A portion of this mixture was placed on a piece of aluminum foil androlled into a sheet with a poly(tetrafluoroethylene) rod. The aluminumfoil with the pressed sheet of the mixture was then placed in aconventional laboratory sublirniation apparatus whose outer wall wasmaintained at 0 C. and the condensation surface was maintained at 78 C.The chilled sheet of the paste-like mixture on the aluminum foil wassubjected of Poly(hexto a vacuum of approximately 1 mm. Hg. for 30minutes. The polyamide sheet which was separated from the aluminum foilwas coherent, microporous, and open-celled and was white, hard andtough. Formic acid or hexafluoroacetone hydrates, used in place ofhexafluoroisopropyl alcohol, give comparable results.

EXAMPLE 3 Microporous Cellular Structure of Polyamide of Different VoidContent A 30 percent (w/v) solution of poly(hexamethyleneadipamide) wasprepared by dissolving g. of the polyamide in 400 ml. ofhexafluoroisopropyl alcohol. Three g. portions of the polyamide solutiondesignated A, B and C were taken. Liquidl,1,1,2-tetrachloro-2,2-difluoroethane, l50 g., 300 g. and 450 g.respectively, were added to each of the three portions of the polyamidesolution. Each mixture was thoroughly mixed and cooled in an ice waterbath, while the mixing was continued. In each case, a thick paste-likemixture was obtained. A portion of each of the three mixtures wassubjected to sublimation as described in Example 1 to form a cellularstructure of polyamide. Another portion of each of the three mixtureswas coagulated in water and washed with cold running water for 24 hours.Each of the coagulated mixtures was then subjected to sublimation asdescribed in Example 1. (Instead of sublimation, coagulated mixture canalso be aspirated by placing in a Buchner funnel and applying suction.)In each case,microporous cellular structure was obtained with thefollowing void content:

EXAMPLE 4 Microporous Open-Celled Sheet of Polycaprolactam Solidpolycaprolactarn (10 g.), was dissolved in 100 ml. of formic acid.Liquid 1, l l ,2-tetrachloro-2,Z-difluoroethane (200 ml.) was then addedto above solution and the mixture was stirred vigorously. On cooling themixture in an ice bath with continuing stirring, there was obtained athick, paste-like mixture, which was coagulated in cold water and washedwith cold running water for 24 hours. The coagulated mass was pressedinto a sheet and subjected to sublimation as described in Example 1.There was obtained a coherent sheet of cellular polycaprolactam whichwas snow-white, soft and flexible.

EXAMPLE 5 Microporous Open-Celled Sheet of Poly(ethylene terephthalate)Solid poly(ethylene terephthalate) film (40 g.) was cut into smallpieces and dissolved in 200 ml. of hexafluoroisopropyl alcohol. To a l00ml. portion of the solution, 200 ml. of liquidl,l,l,2-tetrachloro2,2-difluoroethane were added and the mixture wasstirred vigorously. On cooling the mixture in an ice bath withcontinuing stirring, there was obtained a thick, paste-like mixture,which was coagulated in cold water and washed with cold running waterfor 24 hours. The coagulated mass was pressed into sheet and subjectedto sublimation as described in Example 1. There was obtained a coherentsheet of cellular poly(ethylene terephthalate) which was snow-white andsomewhat brittle.

EXAMPLE 6 Particulate Open Cellular Structure Of Polyester Solid poly(ethylene terephthalate), (50 g.), was stirred with 500 ml. ofhexafluoroisopropyl alcohol to give a viscous solution resembling anorganosol. To 100 ml. of this solution, 200 ml. of liquid 1,1l,2-tetrachloro-2,2-difluoroethane was added and stirred veryvigorously. On cooling the mixture in an ice bath with stirring, therewas obtained a thick paste-like mixture. Removal of both thechlorofluorocarbon and hexafluoroisopropyl alcohol,as described inExample 1, left a snow-white, barely coherent microporous structure ofthe polyester which crumbled to a fine powder on handling.Hexafluoroacetone hydrates, used in place of the hexafluoroisopropylalcohol, give comparable results.

EXAMPLE 7 Particulate Microporous Open-Celled Polyamide Structure Solidpolyhexamethyleneadipamide, 40 g., was dissolved in 400 ml. ofhexafluoroisopropyl alcohol. To the polyarnide solution, 800 ml. ofliquid l,l,1,2-tetrachloro2,2- difluoroethane was added with stirring.Surface active agent, octylphenoxypolyethoxyethanol (Triton Xl00, Rohmand Haas), 15 g., was then dissolved in the mixture. Simultaneouscooling and coagulation were brought about by addition, with goodagitation, of 400 ml. of ice-cold water. A snow-white, heavy, fine-graincoagulum was obtained which was then filtered and washed with cold wateruntil the odor of hexafluoroisopropyl alcohol was no longer detectable.Aspiration on a Buchner funnel to remove the chlorofluorocarbon yieldeda very fine, fluffy, fibrous, microporous powder of polyamide. Formicacid and hexafluoroacetone hydrates, used in place of thehexafluoroisopropyl alcohol, give comparable results.

The coherent open-celled polymeric structures made by the process of thepresent invention can be used in many applications such as insulatingmaterials in areas of low humidity and low internal pressures; inporomeric materials in which vapor penetration is important, e.g., as aheat-insulating layer of a synthetic shoe-upper material; in syntheticsponges and other articles which must be able to absorb large quantitiesof water or other liquids; and in specialty filters.

The particulate open-celled polymeric structures made by the process ofthe present invention can find application in areas where highlyabsorbent, large surface area powders are used. These applicationsinclude: materials for column, gas and thin layer chromatography;desiccating powders; and filtration adjuvants.

This detailed description has been given for clarity of understandingonly and no unnecessary limitations are to be understood therefrom. Theinvention is not limited to exact details shown for obviousmodifications will occur to one skilled in the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A process for preparing a microporous, cellular, open celledstructure from a normally solid polymer selected from the groupconsisting of polyamide, polyester and polyacetal, said processcomprising the following steps:

a. dissolving at least 0.3 weight per volume percent of the selectedpolymer in a solvent selected from the group consisting ofhexafluoroisopropyl alcohol, hexafluoroacetone hydrate, formic acid, andmixtures thereof to form a polymer solution, with the proviso thatformic acid is utilized either alone or in mixture only when theselected polymer is polyamide;

b. dispersing in the resulting solution from about one to about tentimes its volume of a liquid chlorofluorocarbon or mixture ofchlorofluorocarbons having a boiling point in the range of from about 10to 150 C., a melting point in the range of from about 40 to 125 C., anentropy of fusion of less than 10 calories/K/mole, a plastic flow indexof at least 0.1 g./l0 min. at the reduced temperature of 0.96 to 0.99,and a solubility in water of less than about 2 weight percent at atemperature below the atmospheric boiling temperature of thelowest-boiling component of the polymer solution, to form a dispersion;

c. cooling the dispersion to at least the solidification temperature ofthe lowest-melting chlorofluorocarbon present; and

d. removing the solvent and the chlorofluorocarbon from the mixture.

2. A process according to claim 1 wherein the chlorofluorocarbon ormixture of chlorofluorocarbons is selected from the group consisting of1,1, l ,2,2-pentachloro-2- fluoroethane,1,1,2,2-tetrachloro-1,2-difluoroethane, 1,1, 1,2-tetrachloro-2,2-difluoroethane, 1,1 l -trichloro-2,2,2- trifluoroethane,1,2-dichlorodecafluorocyclohexane, l ,1 ,2,2-tetrachloro-perfluorocyclobutane, l ,2-dichloroperfluorocyclobutane,l-chloroperfiuorocyclobutane, 1 ,1,2-trichlorol,2,2-trifluoroethane, l,l l ,3-tetrafluoro-2,2,3 ,3-

tetrachloropropane, 1,1, 1 ,3 ,3-pentafluoro-2,2,3- trichloropropane, l,l, 1,3 ,3 ,3-hexafluoro-2,2- dichloropropane,1,1,1,4,4,4-hexafluoro-2,2,3,3-

tetrachlorobutane and mixtures thereof.

3. A process according to claim 1 wherein from about 0.3 to about 50weight per volume percent of a normally solid polymer selected from thegroup consisting of polyamide, polyester and polyacetal is dissolved inthe selected solvent.

4. The process of claim 1 in which the solvent is removed by evaporationand the chlorofluorocarbon is removed by sublimation at a temperature offrom about 0 C. to the solidification temperature of thechlorofluorocarbon.

5. The process of claim 1 further comprising mixing water with thecooled dispersion of claim 1(c) to form a solventwater phase and apolymer-chlorofluorocarbon mixture, removing the solvent-water phase bydecantation; and removing the chlorofluorocarbon by sublimation at atemperature of from about 0 C. to the solidification temperature of thechlorofluorocarbon.

6. The process of claim 1 further comprising mixing water with thecooled dispersion of claim 1(c) to form a solventwater phase and apolymer-chlorofluorocarbon mixture; removing the solvent-water phase bydecantation; removing substantially all of the chlorofluorocarbon byaspiration at a temperature at which the chlorofluorocarbon is liquid;and removing any residual chlorofluorocarbon by vaporization.

7. The process of claim 1 in which the starting polymer is selected fromthe group poly(hexamethyleneadiparnide), poly(ethylene terephthalate)and polyoxymethylene.

8. The process of claim 1 in which the chlorofluorocarbon is at leastone of l,l,2,2-tetrachloro-l,Z-difluoroethane and 1 ,11,2-tetrachloro-2,2-difluoromethane.

9. A process of claim 1 in which the amount of the chlorofluorocarbonused is such that the resulting polymeric microporous, open-celled,cellular structure is coherent.

10. A process of claim 1 in which the amount of the chlorofluorocarbonused is such that the resulting polymeric microporous, open-celled,cellular structure is particulate.

11. A process according to claim 1 further comprising adding to thedispersion of the chlorofluorocarbon in the polymer solution prior tothe cooling step a chlorofluorocarbon miscible anionic, cationic ornonionic surfactant in an amount of up to 3 weight per volume percent ofsaid dispersron.

12. A process according to claim 11 wherein the surface active agent isanionic and is selected from the group consisting of fatty carboxylicacids, sulfuric esters, alkane sulfonic acids and alkylarylsulfonicacids.

13. A process according to claim 11 wherein the surface active agent iscationic and is selected from the group consisting of fatty amines andquaternary ammonium compounds.

14. A process according to claim 1 1 wherein the surface active agent ismonionic and is selected from the group consisting of polyoxyalkyleneethers of higher fatty acids and alkylphenols.

15. A dispersion of a polymer selected from th group consisting ofpolyamide, polyester and polyacetal prepared by a. dissolving at least0.3 weight per volume percent of the selected polymer in a solventselected from the group consisting of hexafluoroisopropyl alcohol.hexafluoroacetone hydrate, formic acid, and mixtures thereof to form apolymer solution, with the proviso that formic acid is utilized eitheralone or in mixture only when the selected polymer is polyamide, and

(b) dispersing in the resulting solution from about one to about timesits volume of a liquid chlorofluorocarbon or mixture ofchlorofluorocarbons having a boiling point in the range of from about 10to 150 C., a melting point in the range of from about 40' to 125 C., anentropy of fusion of less than 10 calories/"K/mole, a plastic flow indexof at least 0.1 g./1O min. at the reduced temperature of 0.96 to 0.99,and a solubility in water of lea than about 2 weight percent at atemperature below the atmospheric boiling temperature of thelowest-boiling component of the polymer solution, to form a dispersion.

16. A dispersion according to claim wherein the chlorofluorocarbon ormixture of chlorofluorocarbons is selected from the group consisting of1 ,1 1 ,2,2-pentachloro-2- fluoroethane,l,l,2,2-tetrachloro-1,Z-difluoroethane, 1,1 1 ,2-tetrachloro-2,2-difluoroethane, 1 ,l,1-trichloro-2,2,2- trifluoroethane,1,2dichlorodecafluorocyclohexane, 1,1 ,2,2-tetrachloro-perfluorocyclobutane, 1 ,2-dich1oroperfl uorocyclobutane,l-chloroperfluorocyclobutane, 1,1 ,2'trichloro- 1,2,2-trifluoroethane, 1,1,1,3-tetrafluoro-2,2,3,3-

tetrachloropropane, 1,1,1 ,3,3-pentafluoro-2,2,3- trichloropropane, 1,1,1,3,3,3-hexafluoro-2,2- dichloropropane, 1,1,1,4,4,4-hexa.fluoro-2,2,3,3-

tetrachlorobutane and mixtures thereof.

17. A plastic, pliable, moldable, and extrudable composition of matterobtained by a. cooling the dispersion of claim 15 to at least thesolidifcation temperature of the lowest-meltin g chlorofluorocarbonpresent; b. mixing with the cooled dispersion sufiicient water tosubstantially precipitate the polymer; and c. removing the solvent-waterphase.

t t k t

2. A process according to claim 1 wherein the chlorofluorocarbon ormixture of chlorofluorocarbons is selected from the group consisting of1,1,1,2,2-pentachloro-2-fluoroethane,1,1,2,2-tetrachloro-1,2-difluoroethane,1,1,1,2-tetrachloro-2,2-difluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane,1,2-dichlorodecafluorocyclohexane,1,1,2,2-tetrachloro-perfluorocyclobutane,1,2-dichloroperfluorocyclobutane, 1-chloroperfluorocyclobutane, 1,1,2-trichloro-1,2,2-trifluoroethane, 1,1,1,3-tetrafluoro-2,2,3,3-tetrachloropropane, 1,1,1,3,3-pentafluoro-2,2,3-trichloropropane,1,1,1,3,3,3-hexafluoro-2,2-dichloropropane,1,1,1,4,4,4-hexafluoro-2,2,3,3-tetrachlorobutane and mixtures thereof.3. A process according to claim 1 wherein from about 0.3 to about 50weight per volume percent of a normally solid polymer selected from thegroup consisting of polyamide, polyester and polyacetal is dissolved inthe selected solvent.
 4. The process of claim 1 in which the solvent isremoved by evaporation and the chlorofluorocarbon is removed bysublimation at a temperature of from about 0* C. to the solidificationtemperature of the chlorofluorocarbon.
 5. The process of claim 1 furthercomprising mixing water with the cooled dispersion of claim 1(c) to forma solvent-water phase and a polymer-chlorofluorocarbon mixture, removingthe solvent-water phase by decantation; and removing thechlorofluorocarbon by sublimation at a temperature of from about 0* C.to the solidification temperature of the chlorofluorocarbon.
 6. Theprocess of claim 1 further comprising mixing water with the cooleddispersion of claim 1(c) to form a solvent-water phase and apolymer-chlorofluorocarbon mixture; removing the solvent-water phase bydecantation; removing substantially all of the chlorofluorocarbon byaspiration at a temperature at which the chlorofluorocarbon is liquid;and removing any residual chlorofluorocarbon by vaporization.
 7. Theprocess of claim 1 in which the starting polymer is selected from thegroup poly(hexamethyleneadipamide), poly(ethylene terephthalate) andpolyoxymethylene.
 8. The process of claim 1 in which thechlorofluorocarbon is at least one of1,1,2,2-tetrachloro-1,2-difluoroethane and1,1,1,2-tetrachloro-2,2-difluoromethane.
 9. A process of claim 1 inwhich the amount of the chlorofluorocarbon used is such that theresulting polymeric microporous, open-celled, cellular structure iscoherent.
 10. A process of claim 1 in which the amount of thechlorofluorocarbon used is such that the resulting polymericmicroporous, open-celled, cellular structure is particulate.
 11. Aprocess according to claim 1 further comprising adding to the dispersionof the chlorofluorocarbon in the polymer solution prior to the coolingstep a chlorofluorocarbon miscible anionic, cationic or nonionicsurfactant in an amount of up to 3 weight per volume percent of saiddispersion.
 12. A process according to claim 11 wherein the surfaceactive agent is anionic and is selected from the group consistinG offatty carboxylic acids, sulfuric esters, alkane sulfonic acids andalkylarylsulfonic acids.
 13. A process according to claim 11 wherein thesurface active agent is cationic and is selected from the groupconsisting of fatty amines and quaternary ammonium compounds.
 14. Aprocess according to claim 11 wherein the surface active agent ismonionic and is selected from the group consisting of polyoxyalkyleneethers of higher fatty acids and alkylphenols.
 15. A dispersion of apolymer selected from th group consisting of polyamide, polyester andpolyacetal prepared by a. dissolving at least 0.3 weight per volumepercent of the selected polymer in a solvent selected from the groupconsisting of hexafluoropropyl alcohol, hexafluoroacetone hydrate,formic acid, and mixtures thereof to form a polymer solution, with theproviso that formic acid is utilized either alone or in mixture onlywhen the selected polymer is polyamide, and (b) dispersing in theresulting solution from about one to about 10 times its volume of aliquid chlorofluorocarbon or mixture of chlorofluorocarbons having aboiling point in the range of from about 10* to 150* C., a melting pointin the range of from about -40* to 125* C., an entropy of fusion of lessthan 10 calories/*K/mole, a plastic flow index of at least 0.1 g./10min. at the reduced temperature of 0.96 to 0.99, and a solubility inwater of less than about 2 weight percent at a temperature below theatmospheric boiling temperature of the lowest-boiling component of thepolymer solution, to form a dispersion.
 16. A dispersion according toclaim 15 wherein the chlorofluorocarbon or mixture ofchlorofluorocarbons is selected from the group consisting of1,1,1,2,2-pentachloro-2-fluoroethane,1,1,2,2-tetrachloro-1,2-difluoroethane,1,1,1,2-tetrachloro-2,2-difluoroethane,1,1,1-trichloro-2,2,2-trifluoroethane, 1,2dichlorodecafluorocyclohexane,1,1,2,2-tetrachloro-perfluorocyclobutane,1,2-dichloroperfluorocyclobutane, 1-chloroperfluorocyclobutane, 1,1,2-trichloro-1,2,2-trifluoroethane,1,1,1,3-tetrafluoro-2,2,3,3-tetrachloropropane,1,1,1,3,3-pentafluoro-2,2,3-trichloropropane,1,1,1,3,3,3-hexafluoro-2,2-dichloropropane,1,1,1,4,4,4-hexafluoro-2,2,3,3-tetrachlorobutane and mixtures thereof.17. A plastic, pliable, moldable, and extrudable composition of matterobtained by a. cooling the dispersion of claim 15 to at least thesolidification temperature of the lowest-melting chlorofluorocarbonpresent; b. mixing with the cooled dispersion sufficient water tosubstantially precipitate the polymer; and c. removing the solvent-waterphase.